Go Back   Physics Help Forum > High School and Pre-University Physics Help > Energy and Work

Energy and Work Energy and Work Physics Help Forum

LinkBack Thread Tools Display Modes
Old Nov 22nd 2015, 04:23 PM   #1
Junior Member
Join Date: Nov 2015
Posts: 2
Post Force/Velocity of a spring

A spring with a force constant of 350 N/m is compressed 12 cm by a 3.0 kg mass. How fast is the mass moving after only 10 cm of the spring is released?
nolanbradshaw01 is offline   Reply With Quote
Old Nov 22nd 2015, 04:35 PM   #2
Senior Member
Join Date: Apr 2015
Location: Somerset, England
Posts: 708
I don't understand this.

If the 3kg mass compresses the spring, why does anything happen when the spring is released?
studiot is offline   Reply With Quote
Old Jul 5th 2016, 08:30 AM   #3
Senior Member
Join Date: Aug 2010
Posts: 269
Studiot, the OP said "A spring with a force constant of 350 N/m". When he said the spring "is compressed 12 cm by a 3.0 kg mass", he clearly does not mean the spring and mass are in equilibrium- that is, it is not the 3.0 kg mass alone that is compressing the mass- because compressing the spring, with spring constant 350 N/m 12 cm= 0.12 m would result in a force of 350(0.12)= 42 N while a 3.0 kg mass has weight 3.0(9.81)= 29.43 N. When what ever additional force is holding that spring at 12 cm is released, there will be a force of 42- 29.43= 12.57 Newtons on the mass.

The simplest way to answer this problem is to use "total energy". We can take the "0" point for potential energy to be at the 12 cm compression point. The mass is sitting there to begin with so its velocity and kinetic energy are 0. The total energy there is 0. Once the spring is released, it loses potential energy so the potential energy of the mass is negative. The change in potential energy of a mass, m, on a spring with spring constant k, with extension x, is -mkx. The kinetic energy is (1/2)mv^2 so the total energy is -mkx+ (1/2)mv^2. Since energy is conserved, we must have -mkx+ (1/2)mv^2= 0. We can divide by m to get -kx+ (1/2)v^2= 0 or v^2= 2kx. Set k= 350, x= 0.10 m, and solve for v.
HallsofIvy is online now   Reply With Quote

  Physics Help Forum > High School and Pre-University Physics Help > Energy and Work

constant, force or velocity, mass, spring, velocity

Thread Tools
Display Modes

Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Spring force question coolbyte Kinematics and Dynamics 1 Mar 23rd 2013 05:27 PM
Spring force and distance krje1980 Kinematics and Dynamics 6 Dec 14th 2012 11:33 PM
centripetal/spring force, need help! darfmore Periodic and Circular Motion 1 Mar 15th 2012 07:14 PM
Force Constant of Spring Need Help sonog4 Periodic and Circular Motion 2 May 8th 2011 10:31 PM
Spring Force dsptl Kinematics and Dynamics 3 Sep 16th 2008 08:33 AM

Facebook Twitter Google+ RSS Feed